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I currently own a Burnham brand boiler that is a 240,000 BTU input. The house is large and i have been told that it is adequate. I am going to add an indirect water weater to the unit and have been told several different ways of doing it. I need to know what the "best" way is and what will be the most beneficial? Do I need it to be on a priority zone so the heat to the other three zones temporarily shuts off while this tank requires heat? Does it need it's own Pump or can the B&G pump i currently have be used? DO i need some type of circulator added? Any help would be fantastic.

My other is issue is what are the benefits to upgrading to a boiler with a modulating burner. I believe that it basically varies the input as needed and have been told it is the best way to go. Should i upgrade to a 90% efficient unit? What are the top brands in the industry. I always though Burnham was one of the best.

The best way is to determine the heat loss of the house before adding the indirect. If the boiler has enough reserve capacity, you do not need to put the tank on a priority zone.
Yes it does need it's own circulator.
If your existing boiler is in good shape you could likely save a significant amount of money by adding an outdoor reset control. This modulates the boiler temperature with the outdoor temperature.
Upgrade to a 90%? Depends on how efficient your existing boiler is. Burnham doesn't make a 90+ that large. Buderus makes a wall hung 90+ up to 198,800 btu/hr input. Weil-McLain also makes 90+ boilers up to the the size you need but they seem to have recall after recall for one thing or another.

At 28 years old, yes, I would look at a new unit for higher efficiency and peace of mind.

The smart thing to do is this: If the boiler needs to be that big (and I would do a heat loss calc to be sure) and it really needs to be that big ( I know, I've said it again) then I would do multiple boilers, staged. With gas, there are so many options in 90+ units, and controls to do this.

The reason you don't find too many monster 90+ boilers is that it is not intelligent, and it is wasteful to have one huge boiler running zones in a residential application. If only one or two zones call, the dumb boiler doens't know this, it tries to ram it's mega BTU's down the pipe. Short cycles ensue, and fuel consumption soars, and the equipment dies an early death. Modulation helps, like with the Munchkin 199M or the 399M, but when you have a bunch of zones, the things will modulate too much. Equipment design is key.

Modulating or not, if you are looking at loads over, say, 180K+ it really makes sense to split up the boilers and stage them so that the powerplant(s) can match the load. This is especially good for the gonzo indirect water heaters used these days for the human carwashes people "have to have".

When you do the load calc, and you find that your boiler needs all of the BTU's it can put out for heat, then you must prioritize the indirect. If you find that it is bigger than the heat loss then I would prioritize anyway to be sure all the available BTU's are going to the indirect for best recovery.

Always put the indirect on it's own circ. The flow requirements are sometimes different than the heating circ's. You do not want to wait for a zone valve to open, turn on an end switch, then start the boiler (maybe). You want that boiler to instantly start, and begin to make recovery on the hot water. Piping and circ is usually bigger than typical 3/4" pipe for proper flow to the indirect.

If you've done any insulation improvements like new windows, doors, siding and attic insulation, you might not need that large a boiler. I would go with a Munckin or WM Ultra if you still need over 200K BTU's. You should only need the full output if all zones where calling for heat at the same time. With such a large boiler, you'll heat an indirect quickly on priority. If you don't go modulating, look at an indirect like the Ergomax, Turbomax or Dunkirk Artesian. Use the indirect as a buffer tank for when only the smaller zones call for heat.

Boiler blues

Ok, Here's the deal. I have done a huge amount of insulation upgrades in the home. The interior now has all R10 triple pane widows, my attic insulation is up to about an R40+ and the exterior has been covered with 3/4" of concrete stucco. I'm pretty darn tight and in good shape at this point. I'm perplexed as to why no one has offered this wisdom of a heat caluclation? How is it figured? There is really no way of adding an additional boiler to the existing home unless it went in the same room as the other. Perhaps i need a much smaller boiler anyhow according to this info? Is there a charge for a heat calculation? I have a bi-level type home with a third level over the garage where the master bedroom is. Each floor has its own zone. The square footage of the home is approximately 4200. Big, but not overly huge as I may have portrayed. I'm happy to spend the money I need to in order to make this the best situation. I've done a lot over the past 6 years in tightening it up and want to spend another 20 years in this house. Money is tight, but I wnat to doe what's right and makes sence, not what's cheap.

I appreciate all your help, but it appears i need more, possibly more defined, input to do this right. Thanks!

I should also like to add that the larger (80 gal) indirect tank is for a bathtub that gets used nightly by two kids and a wife. It hold 120 gallons filled. We certainly don't fill it anywhere near the top, especially with a standard 50 gal gas tank at present. We just want to have enough water for the tank at all times. Two baths in a rwo with kleen water and possibly a shower or doing dishes would be a dream!

i agree with hydro
with the size af your and all the improvements you have made it makes sense to pull that old war dog out the 27 years old it might only be about 70 percent effecient and at that btu factor burns a lot of fuel with 1 or 2 zones calling, inderict heater in the best way to go in the case i have one and never run out of hot water and have never had a complaint from any one . twin two 140,000 btu two gether and have them cycle as needed for the btu you need when you need it. in the long run you feul bill should be less. the water heater should have it own circulator and be on priority with most inderect it takes about 15 to 20 minutes to recover you will never feel it in the temp of the house

What is your fuel source? I assume its gas. But assumptions can cost.
Have you had a combustion effeciency test done on your current boiler?
You could do your own heat loss calculation with the software avaliable at the top of this page it's a great and easy program.You can download a trial version to check it out and then buy a one time use for a very reasonable price. I would also want my contractor to do his own to double check. search this site for; load calc and manual j, and read up you will get the best education money can buy for free.

Checkout the software for sale on this site. Or expect to pay for someone's time. I'm sure you'll come in under 200K BTU's even with indirect on priority. Get a single top of the line 90% eff modulating condensing gas boiler like the Ultra or Munchkin. No economic sense in getting 2 boilers.